Group B Streptococcus (GBS) is an important human pathogen. At-risk populations include babies born to colonized mothers, peripartum women, diabetics, and the elderly with underlying illnesses. Vaccines to prevent GBS disease have been developed by coupling capsular polysaccharide (CPS) antigens of GBS to immunogenic protein carriers. Glycoconjugate vaccines against all nine GBS serotypes have been synthesized and shown to be immunogenic in animals in preclinical trials. Healthy adults have safely received conjugate vaccines prepared with GBS types la, Ib, II, III, and V CPSs in phase 1/2 clinical trials. These vaccines elicited CPS-specific antibody that opsonized GBS for in vitro killing by human blood leukocytes in the presence of complement. Despite these advances, a GBS vaccine for public use has not been developed due to the number of components required and the shifting pattern of serotypes in the population. Advances in vaccine development has been accelerated by the sequencing of the GBS genome and new protein antigens have been revealed using reverse vaccinology. This proven approach to vaccine development promises to be applicable to GBS vaccines. In this application, we propose to develop a combination vaccine composed of 3 to 4 recently identified protective proteins combined with GBS glycoconjugates representing the three major disease causing serotypes which will be effective against the large majority of GBS variants of all GBS serotypes. A systematic approach will: a) identify, express and purify GBS proteins, b) assess the conservation of these proteins among GBS strains, c) synthesize and test conjugate vaccines in animals using the new GBS antigens as carrier proteins, d) formulate and determine the efficacy of a multivalent GBS vaccine. Successful completion of these objectives will provide the rationale for: e) preparation of a multivalent GBS vaccine made under cGMP, and f) phase 1/2 clinical trials of a multivalent GBS vaccine in healthy nonpregnant (18 to 65 years of age) and elderly (>65 years of age) adults. This work will lead to a vaccine effective in preventing GBS diseases worldwide.